I'm in the same position as you, but really don't feel the urge to get annoyed over it.
Sure if something I type *should* have been resolved, and doesn't due to Virgin, I'd have a mard - but seeing a page of adverts over a 'not found' message, isn't really destroying my quality of life.
Moreover I can see there being value in gathering info on what people have tried that doesn't resolve - using this for *something* productive does appeal (basically, if I were Virgin I'd do the same, so can't blame them for doing it).
I have however plenty of actual gripes with Virgin - fucking about with caps, caching youtube badly, pandering to site blocking requests etc etc etc.
But, by and large, they're a pretty good ISP given their size. I also feel slightly guilty over my wife haranguing them over out 'internet being down' - when it turned out I'd stuffed up the cat wiring in the house. Lovely offshore support guy was very tolerant of her abuse, and resisted inflicting my deserved raking-over-the-coals as the phone was passed over to me and the penny finally dropped.
I'm now off to see if there's anyway I can go and give him a medal..